In order to reduce noise mixed in moving images, there has been used from the past a technology called 3-dimensional noise reduction (3DNR). The 3DNR is a technology to reduce noise by mixing two two-dimensional (2D) frames that are continuous on a time axis. In the 3DNR, in general, each time an input frame is input, an image processing apparatus mixes an output frame previously output and the current input frame, to generate a current output frame. In this mixing, the following image processing apparatus is proposed: the previous output frame and the current input frame are compared with each other to obtain a motion amount, and as the motion amount becomes larger, a mixing ratio of the previous output frame is made lower (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-open No. 2010-4266